The present invention relates to the field of semiconductor wafer processing; more particularly, the present invention relates to cleaning semiconductor substrates (wafers).
Semiconductor manufacturers use semiconductor wafers as the base for manufacturing integrated circuits. In one step of the manufacturing process, the wafers are put through chemical mechanical polishing (CMP). CMP is becoming the main planarization technology for both dielectric and metal layers. For the CMP of dielectric layers, such as BPSG, BPTEOS, and PECVD Oxides (often referred to as the ILD0, ILD1, ILD2 . . . layers, respectively), a fumed silica-based slurry is normally used. Other slurries, such as dispersed silica, fumed or dispersed allumina, are also being used for CMP of both oxides and metals (such as tungsten (W) and titanium (Ti)). When the CMP process is completed, the wafers"" surfaces are covered in particles, referred to as a slurry residue. At later steps in the process flow, some of this slurry residue is redistributed across the front of the wafer, thereby resulting in a loss in die yield and/or device performance. To prevent the slurry redistribution, all surfaces of a wafer must be free of contamination.
Different post CMP cleaning methods have been introduced in the last few years. These include cleaning the wafers in wet stations using conventional wet cleaning methods, such as SC1, HF and megasonic cleaning. Other cleaning methods in use are based on scrubbing wafers with brushes of various kinds and configurations using DI water or a combination of DI with chemicals such as Ammonia and Citric acid.
One system used to remove wafer contaminants is a double sided scrubber. In a double sided scrubber, a semiconductor wafer is scrubbed simultaneously on both sides by brushes. Since the wafer is being scrubbed simultaneously on both sides by the brushes, there must be a way of holding the wafer in place and rotating the wafer so the entire surface of the wafer is cleaned. A mechanism used for this purpose is commonly referred to as a roller.
Today, double sided scrubbers are usually automated and comprise a conveyor type mechanism, rollers, and brushes. In general, the wafer lies flat on the conveyor mechanism and the conveyor mechanism moves the wafer into the brushes. While being scrubbed, the wafer is supported (or held horizontally) by the conveyor mechanism, brushes, rollers, or a combination thereof. FIG. 1 illustrates a conventional double sided wafer scrubber. Referring to FIG. 1, a wafer 101 is being scrubbed by brushes, one of which is shown as brush 102 and the other being beneath wafer 101 and directly below brush 102. Rollers 103 rotate wafer 101 so the entire wafer surface may be cleaned. Each of brushes 102 is rotated about its central axis by a motor 104. The rotary motion of rollers 103 is then transferred to wafer 101 when the edge of each of rollers 103 comes into contact with the outer edge of wafer 101.
Brush cleaning systems can effectively clean the front and backs of semiconductor substrates. However, brushes do not provide a sufficient amount of mechanical energy at the edge/bevel to remove contamination. In other words, although the double sided scrubbers are extremely effective at cleaning the front and back side of a wafer, they can leave a slurry residue on the bevel. Likewise, all of the above methods fail to clean the very edge and bevel area of the substrate (wafer) as well. In other words, all current scrubbing methods and apparatus are unable to clean the very edge and bevel area of the substrate (wafer).
The present invention provides a method and apparatus that cleans the edge of substrates, including the bevel area when present.
A method and apparatus for cleaning edges of substrates is described. The present invention provides a cleaning mechanism that cleans particles off the edge of the wafer based on friction and/or a difference in tangential velocity at a point of contact between the wafer and the cleaning mechanism.